40 CFR § 61.03 - Units and abbreviations.

---
identifier: "/us/cfr/t40/s61.03"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 61.03 - Units and abbreviations."
title_number: 40
title_name: "Protection of Environment"
section_number: "61.03"
section_name: "Units and abbreviations."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "61"
part_name: "NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401"
regulatory_source: "38 FR 8826, Apr. 6, 1973, unless otherwise noted."
cfr_part: "61"
---


# 61.03 Units and abbreviations.

Used in this part are abbreviations and symbols of units of measure. These are defined as follows:

(a) System International (SI) units of measure:

A = ampere

g = gram

Hz = hertz

J = joule

K = degree Kelvin

kg = kilogram

m = meter

m
<sup>2</sup> = square meter

m
<sup>3</sup> = cubic meter

mg = milligram = 10<sub>−3</sub>gram

mm = millimeter = 10<sub>−3</sub>meter

Mg = megagram = 10
<sup>6</sup>gram

mol = mole

N = newton

ng = nanogram = 10<sub>−9</sub>gram

nm = nanometer = 10<sub>−9</sub>meter

Pa = pascal

s = second

V = volt

W = watt

Ω = ohm

µg = microgram = 10<sub>−6</sub>gram

(b) Other units of measure:

°C = degree Celsius (centigrade)

cfm = cubic feet per minute

cc = cubic centimeter

Ci = curie

d = day

°F = degree Fahrenheit

ft
<sup>2</sup> = square feet

ft
<sup>3</sup> = cubic feet

gal = gallon

in = inch

in Hg = inches of mercury

in H<sub>2</sub>O = inches of water

l = liter

lb = pound

lpm = liter per minute

min = minute

ml = milliliter = 10<sub>−3</sub>liter

mrem = millirem = 10<sub>−3</sub> rem

oz = ounces

pCi = picocurie = 10<sub>−12</sub> curie

psig = pounds per square inch gage

°R = degree Rankine

µl = microliter = 10<sub>−6</sub>liter

v/v = volume per volume

yd
<sup>2</sup> = square yards

yr = year

(c) Chemical nomenclature:

Be = beryllium

Hg = mercury

H<sub>2</sub>O = water

(d) Miscellaneous:

act = actual

avg = average

I.D. = inside diameter

M = molar

N = normal

O.D. = outside diameter

% = percent

std = standard

[42 FR 51574, Sept. 29, 1977, as amended at 54 FR 51704, Dec. 15, 1989]